Field of the Invention
The present invention relates to mass flow monitoring of materials, including agricultural materials and food products. More particularly, though not exclusively, the present invention relates to a method and apparatus for using x-ray techniques for monitoring flow rate of materials including biological materials.
Flow rate measurement of agricultural materials and food products is a subject that appears frequently during harvesting, handling and transportation, and in food processing, conveying, and storage stages. While measuring the amount of crop being loaded to/from various transportation vehicles is important for obvious reasons, knowing the amount of material flowing into various physical or chemical processes at food processing plants is vitally important for a proper blend of various elements to go into these processes. In addition to these, in farming, crop flow rate measurement is a subject to growing interest at the harvest stage as well. This forms an important element of a new concept known as precision farming briefly described below.
There is considerable spatial variability in soil properties such as nutrient availability and pH levels within a given field. Factors such as water availability, poor drainage, and variations in topography introduce other dimensions to spatial variabilities resulting in varying yield patterns within a single field. These variabilities traditionally have not been taken into account when practicing soil and crop management. Applying uniform input rates of fertilizers and chemicals may result in excessive agrochemical deposition in some of the areas of a field depending on local requirements. Conventional farm management thus contains two major drawbacks. First, higher application rates than necessary in a certain location would increase the application cost. Second, excessive input application causes surface and groundwater contamination through surface runoff and chemical leaching.
Therefore, it makes more sense to vary application rates of agricultural inputs depending upon the localized needs in a field. This management strategy would help optimize yield obtained from locations having different fertility levels. Thus, as opposed to field-based practices, variable rates of physical and chemical inputs (such as seeds, water, fertilizers and chemicals, and tilling of the soil) should be applied to different areas of a field. In order to achieve this goal, regions of a field with the same yield potential need to be mapped. Creating management zones (small management areas) would help identify the cause-and-effects of the local yield variability. Geographic Information Systems (GIS) can be used to store the spatial soil and yield data, analyze and display results in the form of tables and/or maps, and identify most promising crop and management practices.
The adoption of precision farming includes two major thrusts. One involves the evaluation of outcomes of certain physical and chemical procedures implemented in the field on the basis of databases formed through data acquisition over years. The data acquisition includes yield data in order to generate crop yield maps. Agricultural crop flow measurement is a key parameter in forming yield maps, and accurate measurement of flow rate has a lasting impact on forming reliable databases to be used in precision farming. The second thrust involves development of new machinery, equipment, and sensors to be used in precision farming practices. Specifically, the development of more advanced sensors for data acquisition is very important and will have a lasting impact on overall precision farming activities.
To practice site-specific farming (also known as prescription farming, precision farming, site-specific management, spatially variable farm management, and variable rate technology (VRT)), the position of farm equipment must be determined accurately in real-time while working in the field. By knowing the precise location of the farm equipment, inputs can be applied using predetermined application rates. Amongst various position determination methods, Differential Global Positioning System (DGPS) is the most effective means of 3-D positioning. The location data can be tagged with spatial data to generate maps of applications rates, yield, moisture, pH, and other variables of interest.
The cause-and-effects of yield need to be determined to be able to optimize yield spatially and to reduce environmental contamination due to chemical applications. This requires accurate mass flow rate measurement for materials being harvested since yield maps provide understanding about crop response to various crop management practices in a specified management zone.
Many methods have been used in an attempt to measure flow rates of agricultural products. Two types of yield monitors have been used in the prior art: mass flow meters and volumetric flow meters. Mass flow meters determine the mass of flowing material continuously. Volumetric flow meters are used to measure the volume of product on-the-go as well. The measured volume is converted into standard mass by the manipulation of appropriate conversions.
Commercial volume-based sensors include a paddle-wheel sensor and an infrared sensor (photo-optical sensor). Research prototypes of volumetric sensors include an ultrasonic sensor and Light Emitting Diodes (LED). Commercial mass flow rate sensors available to farmers are impact-based plate sensors (strain-gage based load cells, weigh pads, and potentiometers), a nuclear sensor (gamma ray sensor), and conveyor belts. Examples of research prototypes of mass flow sensors include a change of momentum plate, a pivoted auger, a piezo-film based sensor, and a capacitive sensor. These prior art sensors are described briefly below.
A nuclear sensor (gamma ray) system consists of a gamma ray emitter, a detector, and a display unit. The material flows through a measuring gap between the emitter and detector. The number of photons registered by the detector is reduced by the material as it flows through the sensing volume. Material flow is calculated by the reduction of the number of photons. One problem with nuclear sensors relates to safety. Nuclear sensors use isotopes that require careful handling and extensive shielding. For example, for a nuclear sensor operating at 660 keV, shielding of approximately xc2xd inches of lead or 6-7 inches of steel may be required.
An impact-based sensor system may include strain-gage load cells, weigh pads (platform scales), and potentiometer load cells. All of these sensors use the same principle in determining the mass flow rate of agricultural product. These sensors measure the force exerted by the material as the material hits the sensing element, which is related to the flow rate of the material.
A change of momentum sensor includes a curved plate mounted at the exit of the clean gain elevator of a combine. Friction and impact forces change the direction of the material, such as an agricultural product, on the curved plate. The momentum of the agricultural product changes as the direction is forced to change on the flowing material. The difference in the average material speed is maintained constant between the inlet and outlet of the sensor. The mass flow rate is directly proportional to the force measured by a force transducer attached to the curved plate.
A capacitive sensor works on the principle that the dielectric constant of air/material mixture increases with increasing material concentration in a transport tube. The concentration of the material is determined by using capacitor plates around the transport tube. This method is claimed to be non-intrusive and insensitive to transmitted vibration. Calibration depends on the material being measured and varies with material distribution within the sensor.
With pivoted auger sensors, one end of an auger is supported by a load cell and the other end is pivoted. Agricultural product flows off the agricultural product auger into the pivoted end. The material is then carried by the pivoted auger and is discharged to a tank. The load cell mounted at the end of the pivoted auger measures the flow rate of the grain. The major drawback of this system is space limitations.
Belt conveyors are used primarily for potatoes, tomatoes, peanuts, sugar beets, and other agricultural products harvested with a conveyor belt. Load cells installed beneath the moving belt measure the amount of material being transported.
A piezo-film based impact sensor includes piezo-fum strips (high polar Poly-Vinylidene Film (PVDF)) which are mounted under sieves of combines. The impact of individual kernels are recorded as a measure of agricultural product flow rate. The sensor samples a portion of the material from the sieve.
A paddle wheel sensor consists of a number of paddle wheels. When agricultural product, for example, accumulates and reaches a certain height, the paddles are rotated by an electromagnetic clutch. The flow rate is determined by multiplying the number of revolutions per unit of time and the volume of the paddle wheel. The volumetric flow rate is converted to mass flow rate by using the density of the material being measured.
A photo-optical sensor is mounted near top of the clean grain elevator. The time interrupt of an infrared beam targeted at moving agricultural product is measured. This technique is used to estimate the volume of the flowing material.
An ultrasonic sensor is mounted above a collection bin. The ultrasonic sensor determines the depth or the change of depth of agricultural product in the bin. The change of depth is used to calculate the change of volume of agricultural product over a traveled distance.
In a Light Emitting Diode (LED) sensor, a strip of electronic sensors is mounted in the agricultural product bin. As the agricultural product level rises or falls, the sensor sends signals to LEDs which show the height of the agricultural product at certain levels. The volume of the agricultural product is then estimated. The LED measuring system could be equipped with 1, 4, 8, or 16 sensors.
The prior art flow sensors have been used to monitor the flow of agricultural materials such as grains (corn, soybeans, rice, wheat, etc.), high-value crops (potatoes, sugar beets, cotton, etc.), and straw coming out of combine harvesters and grain elevators as well as in feed and food processing plants. The accuracy of the combine flow sensors is claimed by manufacturers to be from 0.5 to 4% when installed and operated properly.
One problem with prior art flow rate sensors relates to the moisture content of biological materials. The dependence by most prior art devices on the moisture content readings introduces calibration for different types of agricultural products. Volume measuring systems require density of product to be known for a conversion into mass and variation of moisture has an impact on the accuracy of this conversion. Density variations may have an impact on the accuracy of momentum-based sensors as well due to the changes in the impact characteristics of materials with varying hardness.
Another problem with flow rate monitoring relates to noise caused by vibration if the monitoring is done on a moving implement or with respect to moving product. Noise impedes improvement in accuracy. When material flow is very small, the noise signal may become dominant. Below some threshold flow value, the flow rate is often assumed to be zero. This reduces the dynamic range of flow rates that can be determined by the agricultural product flow rate monitor.
Another problem with flow rate monitoring relates to the coating of agricultural product flow sensors. Coating problems may occur on certain types of prior art sensors which interact with the material (including soil and weeds, for example) during the agricultural product flow measurement. This reduces the sensitivity of the yield monitor.
Another problem with flow rate monitoring relates to some devices on mobile platforms such as combine harvesters. Depending upon the field slope the equipment is working on, flow characteristics of the crop changes and this has an impact on the accuracy of the measuring device.
Another important issue is the dependency of the yield sensors on frequent calibrations. Anything that changes the way the material flows through the transport system and anything that alters the way the material interacts with the sensing element would have an effect on the calibration accuracy of flow sensors. Thus, changes in material properties and flow dynamics would require recalibration of a yield sensor. Dependency on calibration makes flow rate sensors prone to errors.
Flow rate devices immune to the above problems would have large advantages over the devices requiring frequents calibrations to account for concerns summarized above.
A general feature of the present invention is the provision of a method and apparatus for monitoring product or materials flow, including agricultural product flow, which overcomes problems found in the prior art.
A further feature of the present invention is the provision of a method and apparatus for monitoring product flow that uses x-ray techniques.
Further features, objects, and advantages of the present invention include:
a) A method and apparatus for monitoring product flow which uses x-ray techniques, which monitors the product flow while the product flows at various places such as combine harvesters, grain elevators, food processing plants, etc.
b) A method and apparatus for monitoring product flow which uses x-ray techniques, which does not impede the product flow.
c) A method and apparatus for monitoring product flow which uses x-ray techniques, which does not physically interact with the product itself.
d) A method and apparatus for monitoring product flow which uses x-ray techniques, which has a large dynamic range and a high sensitivity.
e) A method and apparatus for monitoring product flow which uses x-ray techniques, which is insensitive to product moisture content, particularly in agricultural products.
f) A method and apparatus for monitoring product flow which uses x-ray techniques, which is insensitive to product flow profile, as most products, including agricultural products do not fall or flow with the same amount of product across a cross section of the flow.
These as well as other features, objects, and advantages of the present invention will become apparent from the following specification and claims.
The flow rate measurement system of the present invention is an apparatus and method used to determine the flow rate of materials, including biological and agricultural products. The apparatus is comprised of an x-ray generator positioned near a flow of material such as agricultural product, a detector capturing the x-ray energy emitted by the generator and detecting intensity of x-ray radiation after passing through the flow of material, and a processor for processing the image to determine the material flow rate. The invention may optionally include a converter to convert detected x-ray radiation into visible light and/or an image intensifier coupled to or instead of the converter for enhancing intensity of light.
The method is comprised of directing x-ray energy through a flow of material, measuring the intensity of the x-ray energy after passing through the flow of material and correlating the intensity to flow rate of the material.